The present invention relates to a pretensioner for vehicle seat belt systems and, in particular, to a buckle pretensioner of the type having an inertia starting mechanism incorporated into it that has a device for preventing the starting mechanism from operating erroneously.
In some seat belt systems used in vehicles such as automobiles, a pretensioner is provided for preventing movement of the body of an occupant by tightening of the belt when excessive acceleration acts on the vehicle and thereby providing greater restraint of the occupant. Although pretensioners can be provided at various locations in a seat belt system, an advantageous location is at the transition point between the lap and shoulder portions of a belt in a three point belt system. Applying tension to the belt at the transition point tightens both the lap and shoulder belt portions and provides better restraint of the occupant. In most three point systems, there is a buckle tongue at the transition point that is connected to a buckle. It is well known to provide a pretensioner that pulls down on the buckle that receives the buckle tongue at the transition point between the lap and shoulder portions of a seat belt.
One manufacturer of a buckle pretensioner, AUTO-LIV Company, has produced commercially a buckle pretensioner having a built-in mechanical inertial starting device. Ordinarily, the AUTO-LIV buckle pretensioner is installed on the side of the vehicle seat, and it may operate erroneously by an abrupt movement of the seat when its position is changed. Accordingly, a linkage has been established by a wire connected from the seat release lever to the inertia starting mechanism of the pretensioner such that when the seat release lever is moved to a position allowing the seat to move, the inertia starting mechanism is prevented from operating to trigger the operation of the pretensioner.
The linkage between the seat release lever and the pretensioner does not always prevent erroneous operation of the pretensioner. It sometimes happens that after the seat position is changed and the release lever moves back to its normal position, the seat is between latched positions and is not latched against subsequent movement, which can occur without moving the release lever, such as upon abrupt acceleration or sharp braking of the vehicle. Such movements of the vehicle can cause the seat to move suddenly and then be stopped abruptly by engaging a stop of the seat slide latch. The abrupt stopping the seat can result in operation of the inertial starting mechanism such as to actuate the pretensioner.